The present invention relates to an image processor and an image processing method for embedding a digital watermark in image data.
In recent years, due to explosive development and widespread of computers and their networks, a variety of information such as character data, image data and voice data have been digitized. Digital information does not undergo degradation due to secular changes and thus can be stored in perfect state permanently, but it can be easily duplicated and therefore the protection of copyright becomes an important issue. For this reason, security technologies for protecting copyright assume greater importance at a rapid pace.
One of techniques for protecting copyright is a xe2x80x9cdigital watermarkxe2x80x9d. The digital watermark is a technique of embedding the name of a possessor of copyright and the ID of a purchaser in digital image data, voice data, character data and the like in a form imperceptible by persons, and tracking unauthorized use thereof by illegal copying.
The digital watermark may be subjected to variety of attacks. They include, for example, irreversible compression such as JPEG, geometric transformation such as scaling or rotation, printout/scanning and noise attachment.
Here, a process called registration may be used particularly for providing resistance to geometric transformation. Registration is a process of adding a specific signal (registration signal) to an image in addition to added information at the time of embedding the digital watermark, and promoting the extraction of added information using the above described registration signal before added information is extracted, at the time of extracting added information.
Systems using the registration include a system proposed in U.S. Pat. No. 5,636,292. This is a system in which a geometric pattern embedded in advance is used to calculate automatically the geometric transformation applied to the image. In this system, the geometric transformation has a plurality of solutions because the geometric pattern has a symmetric axis, thus making unique identification impossible.
A system to solve this problem is proposed in Japanese Patent Laid-Open No. 11-355547. This system is a system in which as in the case of U.S. Pat. No. 5,636,292, the geometric pattern is used to perform registration, but the geometric pattern is comprised of two-dimensional waves that do not have symmetric axes, and therefore the geometric transformation does not have a plurality of solutions.
In these conventional systems, the registration signal is embedded equally for all images. On the other hand, the image signal may have different frequency properties, and preferred registration devices are not provided for all image signals having different frequency properties.
Also, conventionally, registration signal is embedded as a size equal to that of the entire image. On the other hand, it is desired that a registration signal having maximum amplitude is used for easy extraction, but this results in increased degradation of the image in which the digital watermark is embedded.
The present invention has been made to solve the problems of prior arts described above, and its object is to provide an image processor and an image processing method for embedding a registration signal more appropriately.
According to the present invention, the foregoing object is attained by providing an image processing method of embedding registration signals in image data, comprising: a feature component detecting step of detecting a feature component of the image data; a registration signal selecting step of selecting one registration signal from a plurality of registration signals, in accordance with the feature component; and an adding step of adding to the image data the registration signal selected by the registration signal selecting step.
According to another aspect of the present invention, the foregoing object is attained by providing an image processing method of inputting image data with registration signals embedded therein, subjected to geometric transformation, and extracting registration signals from the inputted image data to perform registration processing, comprising: a registration signal extracting step of extracting registration signals from the image data; a frequency property determining step of determining frequency properties of the image data; a geometric transformation identifying step of identifying geometric transformation to which the image data is subjected, using the extracted registration signals and determination results of the determination in the frequency property determining step; and a geometric transforming step of performing inverse transformation of the identified geometric transformation.
In still another aspect of the present invention, the foregoing object is attained by providing an image processor for embedding registration signals in image data, comprising: feature component detecting means for detecting a feature component of the image data; registration signal selecting means for selecting one registration signal from a plurality of registration signals, in accordance with the feature component; and adding means for adding to the image data the registration signal selected by the registration signal selecting means.
In still another aspect of the present invention, the foregoing object is attained by providing an image processor for inputting image data with registration signals embedded therein, subjected to geometric transformation, and extracting registration signals from the inputted image data to perform registration processing, comprising: registration signal extracting means for extracting registration signals from the image data; frequency property determining means for determining frequency properties of the image data; geometric transformation identifying means for identifying geometric transformation to which the image data is subjected, using the extracted registration signals and determination results of the determination by the frequency property determining means; and geometric transforming means for performing inverse transformation of the identified geometric transformation.
In still another aspect of the present invention, the foregoing object is attained by providing a computer program product embodying a program for implementing an image processing method of embedding registration signals in image data, the program comprising: a program code for the feature component detecting step of detecting a feature component of the image data; a program code for a registration signal selecting step of selecting one registration signal from a plurality of registration signals, in accordance with the feature component; and a program code for an adding step of adding to the image data the registration signal selected by the registration signal selecting step.
In still another aspect of the present invention, the foregoing object is attained by providing a computer data signal embodied in a propagating wave and used for implementing an image processing method of embedding registration signals in image-data, comprising: a code signal for use in a feature component detecting step of detecting a feature component of the image data; a code signal for use in a registration signal selecting step of selecting one registration signal from a plurality of registration signals, in accordance with the feature component; and a code signal for use in an adding step of adding to the image data the registration signal selected by the registration signal selecting step.
In still another aspect of the present invention, the foregoing object is attained by providing a computer program product embodying a program for implementing an image processing method of inputting image data with registration signals embedded therein, subjected to geometric transformation, and extracting registration signals from the inputted image data to perform registration processing, the program comprising: a program code for a registration signal extracting step of extracting registration signals from the image data; a program code for a frequency property determining step of determining frequency properties of the image data; a program code for a geometric transformation identifying step of identifying geometric transformation to which the image data is subjected, using the extracted registration signals and determination results of the determination in the frequency property determining step; and a program code for a geometric transforming step of performing inverse transformation of the identified geometric transformation.
In still another aspect of the present invention, the foregoing object is attained by providing a computer data signal embodied in a propagating wave and used for implementing an image processing method of inputting image data with registration signals embedded therein, subjected to geometric transformation, and extracting registration signals from the inputted image data to perform registration processing, comprising: a code signal for use in a registration signal extracting step of extracting registration signals from the image data; a code signal for use in a frequency property determining step of determining frequency properties of the image data; a code signal for use in a geometric transformation identifying step of identifying geometric transformation to which the image data is subjected, using the extracted registration signals and determination results of the determination in the frequency property determining step; and a code signal for use in a geometric transforming step of performing inverse transformation of the identified geometric transformation.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.